Throughout many regions of the world, heavy oil, a hydrocarbon material having much higher viscosity or lower API gravity (less than 20° API, typically 7° to 12° API) than conventional petroleum crude, is being economically recovered for commercial sale. During the recovery process and prior to the transport to refineries for upgrading, the heavy oil receives preliminary treatment for water and solids removal to generally achieve basic sediment and water (BS & W) content less than 0.5% by volume and chloride content less than 30 ppm (wt). Water content of the treated heavy oil typically is required to be 0.3% by volume or less.
Conventional crude oil treatment methods were proven to be ineffective with respect to heavy oil until the advent of the technology set forth in U.S. Pat. Reissue No. 33,999, Clare et al., reissued Jul. 21, 1992 and Canadian Patent 1,302,937, Clare et al., reissued on Jun. 9, 1992. These patents describe a simple apparatus which can be located in remote oil producing areas for dehydrating heavy oil with low risk of foaming and unstable operating, while continuously achieving dry oil which exceeds requisite specifications. These dehydrators were found to be restricted to feed oil water content of less than 5% water cuts and susceptible to foaming and process instability during high water feed rates. Throughout the operation of several of these dehydrators known from practicing the technology in U.S. Pat. Nos. Re 33,999 and 1,302,937, areas for improvement were discovered to overcome the limitations of feed oil water content and unstable operation caused by pretreatment upsets.
Further, additional problems have been experienced with the prior art in that although dehydrated heavy oil is achieved, high concentrations of suspended solids, such as clay and silica and dissolved compounds such as chlorides remain in the treated oil. These undesirable compounds continue to create many problems in pipeline transportation systems and refinery facilities to the extent that they depreciate the commercial valve of heavy oil.
It has been found in field applications that mineral salts, silica, clay inter alia that remain in the dehydrated crude promote corrosion cracking in stainless steel components and induce scale accretion and/or fouling of surfaces critical to efficient and consistent operation of the apparatus in the refiner and pipeline systems. Generally speaking, the salt crystals mix with the oil and coalescence results to form larger crystals which can pass through the refinery desalination equipment.
Accordingly, one object of the present invention is to provide advances to overcome the limitations encountered by the previous art.